Tool for punching acoustic holes



Aug. 4, 196 D. w. AKERSON TOOL FOR uncams ACOUSTIC HOLES Filed 001'.- l, 1962 Jays A (DRILLED) AIR-DRY DENSITY (POUNDS PER CUBlC F000 United States Patent 3,143,026 TOOL FOR PUNCHENG ACOUSTIC HOLES David W. Akerson, St. Paul, Minn., assignor to Wood Conversion Company, St. Paui, Minn, a corporation of Delaware Filed Oct. 1, 1962, Ser. No. 228,217 8 Claims. (Cl. 83-686) The present invention relates generally. to tools, and in particular, to tools for the manufacture of acoustic bodies or panels, such as wallboard, tile and plank.

Heretofore, porous panel-form bodies which have interior capacity to absorb sound have been drilled with holes to collect sound Waves and transmit them to the interior of the body. The common practice is to drill round holes of such size that they are visible when present in ceiling tile and the arrangement of the holes is such as to form an acceptable pattern.

Where visibility of such holes is undesired, as for example, when other decoration is present at the surface of the tile, a recent practice is to punch small holes with pins or like tools of such cross-section that the holes are practically invisible at viewing distance, or otherwise if visible, constitute such a small portion of the containing area that other decoration at the surface subdues the visible effect of such small holes.

This application is a continuation-in-part of copending application Serial No. 5,808, filed February 1, 1960 now abandoned as a continuation-in-part of copending application Serial No. 765,546, filed October 6, 1958.

In said applications Serial No. 765,546 and Serial No. 5,808, there are described various tools and .methods which may be used toform cavities within a board which are larger than a small orifice or entrance thereto through the facial layersof the board. Among such tools is a particular form which operates by merely inserting it and withdrawing it from fiberboard, in which, when it is formed of vegetable (or cellulosic) fiber, an opening or cavity is formed internally of the board which is greatly enlarged relative to the entrance thorugh the face of the board.

The following description is directed to punching holes in a cellulosic fiberboard having an insulating density of about 17 lbs. per cu. ft., and formed from fibers derived from wood.

Investigation of the variations of punch structures has shown that some punches merely push the fibers aside forming a hole matching the punch in contour. Other punches form a cavity within the board larger in size than the opening formed in the surface by the punch. Other punches delaminate the body of the board. The following observations were made:

Bluntpunches, such as cylindrical rods with a fiat circular end, tend to delaminate the structure by initially pushing an area of felted layers inwardly, which pushed area expands as it moves inwardly and carries with it adjacent structure felted into it. With a diameter of ;-inch, the effect was barely noticeable. At Ai-inch diameter, delamination is easily observed. At W -inch diameter, the punch completely destroyed the neighboring structure of the board.

Pointed punches having a long conoidal taper, with an included angle in the vicinity of 10 to merely form a hole corresponding to the shape of the punch.

Conoidal pointed punches having .an :includedangle vof delaminate the board like a flat-end punch. Pointed punches having a short conoidal taper at an included angle in the vicinity of 30 form within the board a cavity of larger size than the hole formed in the surface, the cavity beingconnected to the exterior by a short tubular channel in the surface layer.

It was discovered that when such a cavity-forming short-tapered punch was provided with a flat end, by grinding off the point, preferably, but not necessarily, at right angles'to the axis of the punch, a pear-shaped cavity is formed near butinwardly from the surface opening and the cavity is larger than when the punch is not flattend and is pointed. 'In some instances, such punches also form-two spaced pear-shaped cavities alined along the path of the punch, the innermost one being the smaller. The presently preferred punch for mechanical reasons as Well as for the formation of cavities-in a cellulosic fiberboard, is a cylindrical one having a diameterof -inch, with a frusto-conical end whichhas a base with a diameter in the range from 0.015 to 0.020 inch and a wall with an included cone angle of 30. The delaminating tendency above referred to is limited and controlled to enhance the cavitizing action of a pointed punch. The effect is measured not by one hole, but by a multiplicity of such holes necessary to create acoustic value. When each hole involves some delamination, this may be so extensive that the total delamination of the multiplicity of holes effectively destroys the structure of the board. The small fiat area of the advancing punch of the present invention is too small to destroy the board when a multiplicity of vpins are used, but it has a rupturing action leading to a larger cavity being formed by the following tapered section. Circular punches as forms of revolution about an axis are preferred so that the cavity formed is more or less symmetrically pear-shaped, and also for mechanical facility in providing a gang-punch and a stripper plate.

Because small openings into the board are contemplated, the shank of the tool is slender and easily bent. Tools which areso formed that in use there is a lateral thrust on the tool, gradually yield to the thrust and bend. This is so when the fiat base is slightly angular to the plane normal tothe axis of the tool. It also takes place when the tapered wall or walls are offset. For this reason, the tapered wall or walls preferably correspond to a cone coaxial with the length of the shank, or to a regular polyhedron coaxial with an axis parallel to the length of the shank. The portion of the shank which enters the board is so shaped that it does not enlarge the opening and the channel made by the large base of the tapered section. Preferably, such portion of the shank is rodform in extension of said base, the shank beyond the penetrating portion is preferably a continuation of said rod form, and said shank portion accordingly beyond the said large base being a plurality of times longer than the tapered section.

In providing a stripper plate, holes therein are formed closely to conform to the pattern of rod-form shanks in a bank of tools, thus to minimize the tendencies of the tools to bend at the levels outside the board. However, the stripper plate does not prevent bending of the insertable portion. When this is bent the opening formed in the board may be elongated relative to the cross-section of the shank.

The action of cavitizing above described in part depends upon the tensile strength and toughness of individual vegetable fibers which are pulled out of their original felted positions in cavitizing, and compressed in the lower part of the cavity. Sometimes, there is a densified body of fiber along the lower portion of a side Wall, and sometimes it is in the bottom of the channel left by the punch.

The cavities formed vary individually in size and shape, apparently as a result of variations locally in the board structure. Sometimes, the internal structure is such that a cavity does not form, but because such fiberboards are relatively homogeneous, the punching of a large number of holes in the same manner assures that substantially all of them have a cavity. The aim is to provide a multiplicity of cavities each connected to at least one surface opening by a channel from the cavity to the opening.

FIG. 1 is a fragmentary perspective view, partly in section, of an acoustic article of vegetable fiber embodying the present invention.

FIG. 2 represents a tool as the preferred form.

FIG. 3 represents a tool similar to that of FIG. 2, with dimensions variable within limits.

FIGS. 4 and 5 represent modified forms of the tool.

FIG. 6 represents a tool as it may be sharpened.

FIG. 7 represents a tool With a modified shank.

FIG. 8 is a graph showing the variation in absorption by a series of products similar to that in FIG. 1, which vary in density.

FIG. 1 represents a fragmentary enlarged view of a cellulosic fiberboard cavitized as described. The body 10 has felted wood fibers bonded by having hydrated the fibers before felting, pressing and drying to a density of about 17 lbs/cu. ft. Such boards are commonly coated for decoration, as indicated by the coat 11 and it is preferred to coat before punching. The coated face is punched as described forming a multiplicity of openings, some being indicated at 12, and others at 13 and 14.

The opening 13 extends as a tubular channel 15 through the coating and through the adjacent layer of the fiber body. Then, the enlarged cavity 16 which is formed is generally pear-shaped tapering away from the surface to a tubular channel 17 substantially matching the drill size. The darkened area 18 represents one location at which a densified fiber mass is deposited. Thus, the cavity has a major portion of its wall area at least as porous as the body of the board.

Some holes formed in the same manner as hole 13, and at the same time in the same board, show two cavities, as illustrated at the opening 14-. The upper cavity 20 corresponds generally to cavity 16, but below it there is a tubular channel 21 generally matching the punch in size which channel 21 enlarges to a cavity 22, smaller than cavity 20, and likewise pear-shaped, which second cavity is extended by tubular channel 23 formed by the end of punch. The local variations in formation account for the different results.

Experience with cavity-forming punches in modification of the preferred punch described above, has established ranges for the essential dimensions of the tool. These ranges take into account the fact that continued use of a tool wears it so that it dimensions change, and the changes could be such that the tool fails to form cavities. The tools of the present invention may be made initially with dimensions within prescribed ranges, and such that after wear they may be dressed with a minimum of shortening to new dimensions still within the ranges,

or shortened to reproduce the original dimesnions.

FIG. 2 represents the above-described preferred tool as shown in said earlier application and therein characterized as having a cylindrical shank 25 -inch in diameter, a coaxial frusto-conical end 26 with an angle of 15 with the axis of the shank, and a base 27 of diameter in the range from 0.015 to 0.020 inches.

For a coaxial tool like that of FIG. 2, the dimensions may be varied, as indicated in FIG. 3. The cylindrical shank 30 has a diameter D in the range from 0.0312 to 0.124 inch to /3 inch). The frusto-conical section 31 has an included angle in the range from 15 to 60, i.e., the cone wall forms an angle 6 with the axis 32 of the shank in the range 7.5 to 30. The coaxial base 33 has a diameter d in the range from .005 to .040 inch.

The shank of the tool need not be cylindrical because the area of the formed hole functions for its acoustic value rather than its shape. The cross-section of the shank may be square, triangular, a crescent, or other irregular form, so long as the area A of the cross-section falls within the area of a circle having a diameter in the said range D, or an area in the range from 0.000765 to 0.0123 sq. inch.

When the tool is shaped differently from that shown in FIG. 3, it is preferred that the cross-section be regular, such as a square or an equilateral triangle, and that the tapered end likewise be regular and coaxial, so as to avoid lateral thrust on the tool in use.

FIG. 4 shows a tool with square shank 35, a frustopyramidal end 36 with its side walls having said angle 0 with the axis 37 of the shank, and with a base 38 having an area a, which varies in the range 0.0000196 to 0.00125 sq. inch, corresponding to said diameter d.

Nevertheless, tools which encounter lateral thrust are not excluded. Such thrust may derive from the base, such as bases 27, 33 and 38, being at an angle other than to the axis of the shank, yet being substantially normal to the axis, or from such a base being laterally offset from a coaxial position. FIG. 5 represents a tool with a laterally offset base. It has a cylindrical shank 40 of diameter D, with axis designated 41, a base 42 of area a at substantially 90 with axis 41, and a conoidal end 43 such that one geometrical element thereof 44 is substantially an extension of a geometrical element of the wall of the shank 40, and such that the greatest angularity of the conoidal end 43 with the axis 41 lies within the range for said angle 6.

An oit-center tool according to FIG. 5 having a cylindrical shank 40 ;-inch in diameter and a tapered end 43 with included angle of 20 and a base 0.02-inch in diameter, forms cavities beginning about As-inch below the surface of the board. Because of lateral thrust the shank flexes and moves laterally producing an elongated opening to the cavity. When the diameter of the tool as above-described is increased to -inch, the described double cavities are sometimes formed.

When the two tools of FIG. 5 above-described in detail are modified so as to have a 30 included angle, single and sometimes double cavities are formed with elongated openings due to flexing of the shank.

Since it is preferred not only to form round openings with a cylindrical shank as well as to preserve the straight character of the tool, the base is normal to the axis of the shank and the tapered end is so related to the shank that punching in the direction of the lengthwise extent of the shank avoids lateral thrust on the tool.

FIG. 6 shows an enlarged view of a tool of the preferred type having cylindrical shank 45 of cross-sectional area A and a worn end shown by full line 46, of which the original form is shown in the outside dotted line as having base 47 of area a" and a coaxial frusto-conical section 48 with a Wall-to-wall angle 1. The interior dotted lines indicate a sharpened end such that there is a new base 49 of area less than a" and a new conoidal wall 50 with new angle 2'. As evident from FIG. 6, the base grows smaller on so sharpening, and the angle z grows larger on so sharpening. In consequence, when the tool is to be sharpened in this manner, the original dimensions are so chosen that the base is near the larger end of its range, and the angle :5 is near the low end of its range. When repeated sharpenings of the type described bring the dimensions of the tool close to a limiting range, the

tool may be sharpened by shortening it to selected dimensions within the limiting ranges.

Since it is the blunted tapered end which forms the cavities, the shank may be considered merely as a handle for the tapered end, having no important other function when inserting the tool. But, on withdrawing the tool, the shank or handle must be such that it provides a path for the tapered end to follow and such that it does not lead to lifting the fibers or a coating on the board at the edge of the entering hole. For this reason, the portion of the shank adjacent the tapered end has a cross-section comprehended within the largest diameter of the tapered end, but without forming a disrupting ledge.

FIG. 7 shows a tool similar to that of FIGS. 3 and 6, in which the tapered end portion 51 has end base 52, largest cross-section or base '53, and shank 54 of changing diameter. Beginning at large base 53, the diameter gradually ensmalls for a length 55 including the length to be inserted into a board, up to a smaller diameter at a junction 56 with a larger diameter shank portion 57, which provides rigidity. It is important that the large base 53 smoothly leave the board without damage to the edge of the hole, as could occur with a ledge (horizontal in the drawing) at said region, such as a shoulder like that at the junction 56, which ledge could chip away a brittle coating on the board.

The dimensions of the tool are coordinated for the desired result. The flat end, the angle of taper, axial extent of taper, and shank cross-section or diameter are all so related, that in use they function as follows: The flat base must have an area to produce a cavity, but without delaminating the structure laterally from the cavity walls. The angle of taper must be such that it enlarges the initial opening by pushing the fibers laterally. The axial length of taper must be so much less than the thickness of the tile that the punch terminates inwardly from the back of the tile and in this position, the tapered portion is inwardly from the face of the tile. The crosssectional area as diameter of the shank is such that the parallel-sided or tubular channel formed by the passage of the tapered portion is small in area to provide a neck for the larger cavity within.

The character of the cavity varies with the density of the board punched. A board of any given density when uncompressed may be compressed within limits and punched while so compressed. Thus, in using a gang punch with a stripper plate through which the punches extend, the character of the cavity may be varied by varying the degree of compression of the board while being punched. This may be accomplished by placing the stripper plate in contact with the face to be punched at varying pressures from zero to some higher pressure, before moving the punches into the board. Pressure of the stripper plate on the punched face is important to prevent lifting of the coating at the edge of a hole by the outwardly moving punch. Compression of a coated board before punching is frequently important to prevent breaking the coat at regions away from the entering punch, depending in part on the density of the board and in part on the character of the coat, for example, its brittleness.

The density of the board is involved in its soundabsorbency. Sound-absorbency is measured in several different ways of which one has been used for testing products of the present invention, namely, the impedance tube test of the American Society of Testing Materials designation C3 8456T. An area of a board is tested for sound in the following frequencies: 250,500, 1,000 and 2,000 cycles per second, and the values averaged as tube test coefiicient, hereinafter referred to as TT C. 7

Wood fiberboards of various densities and of one-half inch thickness, all coated, were gang-punched and cavitized with the preferred V -inch diameter punches with the 30 frusto-conical end previously described in a random arrangement of 578 holes per sq. ft. FIG. 7 shows 6 the TTC for the various densities. The significance of the results is indicated by the fact that substantially the same values are secured by the same test, using boards of the same character drilled in a random manner with 4-inch and %;-inch diameter drills totaling 319 holes per sq. ft., whereas for the non-cavitized punching, much less absorption occurs.

FIG. .8 is a plot of TTC on the Y axis against density of the board on the X axis, the density being for air-dry wood fiberboard in pounds per cu. ft. Graph A represents the TTC for boards with the conventional dnilled holes, with a random and mixed pattern of two sizes of drills, namely, Ar -inch and -inch diameter.

Graph B is a plot of TTC in similar boards cavitized with the preferred type of blunted tapered ,-inch diameter punch above described. It has nearly the same capacity for absorption as the drilled units, but has the advantage of practically invisible openings at viewing distances in a completed installation.

Graph C represents the TTC of similar units punched with non-cavitizing tapered punches of -inch diameter. The appearances of the units for Graphs B and C are identical, and the value of the interior cavities is represented by the higher TTC values of Graph B over Graph C.

I claim:

1. A straight punch for penetrating fiberboard comprising a shank portion for entering the board and a tapered end portion, said punch at the junction of said tapered end portion and said shank portion having a cross-section at least as large as the cross-section of said shank portion, said shank portion being a plurality of times longer than said tapered end portion, said crosssection at said junction having an area in the range from 0.000765 to 0.0123 sq. inch, said punch having a flat end substantially perpendicular to the lengthwise extent of the punch and having an area in the range from 0.0000196 to 0.00125 sq. inch, said side walls of said tapered end portion being angular with an axis parallel to the lengthwise extent of the punch in the range from 7.5 to 30.

2. A punch according to claim 1 in which the tapered end portion has a flat end at with the lengthwise extent of the punch and in which the side walls are identically related to said axis whereby in use to minimize lateral thrust.

3. A punch according to claim 1 in which the tapered end portion is frusto-conical with its axis parallel to the lengthwise extent of the punch.

4. A punch according to claim 1 in which the tapered end portion is frusto-conical with its axis parallel to the lengthwise extent of the punch and the said shank portion is cylindrical and coaxial and has a cross-section the same as that at said junction.

5. A straight punch for penetrating fiberboard comprising a shank portion for entering the board and a tapered frusto-conical end portion with its axis parallel to the lengthwise extent of the punch, said punch at the junction of said tapered end portion and said shank having a circular cross-section of diameter in the range from .0312 to 0.125 inch, said punch having a flat end at 90 to said axis and a diameter in the range from 0.005 to 0.040 inch, said end portion having a conical side wall at an angle with said axis in the range from 75 to 30.

6. A straight punch according to claim 5 in which the shank portion is cylindrical and coaxial with the frusto-conical portion and has a diameter the same as that at said junction.

7. A straight punch for penetrating fiberboard comprising a shank portion for entering the board and a tapered frusto-conical end portion with its axis parallel to the lengthwise extent of the punch, said punch at the junction of said tapered end portion and said shank portion having a circular cross-section of -inch diameter,

7 t' said punch having a fiat end at 90 to said axis and a diameter in the range from 0.015 to 0.020 inch, the shank diameter in the range from 0.015 to 0.020 inch, said portion beyond its junction With said end portion having end portion having an included angle of 30, said shank a'length a plurality of times longer than said end portion. for a distance which is a plurality of times greater than a the distance from said junction to said end having a CrOSs- 5 References Cited in the file of this patent section not greater than its cross-section at said junction. UNITED STATESVPATENTS 8. A straight punch having a cylindrical shank of i -inch diameter and a coaxial tapered frusto-conical $2333 {:2 i? end portion having an included angle of 30 said punch 3:017:947 Eckert 1962 having a flat end at 90 to the axis of the shank with a 10 

1. A STRAIGHT PUNCH FOR PENETRATING FIBERBOARD COMPRISING A SHANK PORTION FOR ENTERING THE BOARD AND A TAPERED END PORTION, SAID PUNCH AT THE JUNCTION OF SAID TAPERED END PORTION AND SAID SHANK PORTION HAVING A CROSS-SECTION AT LEAST AS LARGE AS THE CROSS-SECTION OF SAID SHANK PORTION, SAID SHANK PORTION BEING A PLURALITY OF TIMES LONGER THAN SAID TAPERED END PORTION, SAID CROSSSECTION AT SAID JUNCTION HAVING AN AREA IN THE RANGE FROM 0.000765 TO 0.0123 SQ. INCH, SAID PUNCH HAVING A FLAT END SUBSTANTIALLY PERPENDICULAR TO THE LENGTHWISE EXTENT OF THE PUNCH AND HAVING AN AREA IN THE RANGE FROM 0.0000196 TO 0.00125 SQ. INCH, SAID SIDE WALLS OF SAID TAPERED END PORTION BEING ANGULAR WITH AN AXIS PARALLEL TO THE LENGTHWISE EXTENT OF THE PUNCH IN THE RANGE FROM 7.5* TO 30*. 